For many years, thermostats have had means to limit the adjustment of the temperature control point adjusting means or selection level to some selected value for both heating and cooling operations. Such limiting action has been for limiting the temperature for comfort and for energy conservation. With the advent of even higher energy costs, the need for limiting action in thermostats is even much more emphasized; in fact, certain localities have established laws to restrict the range of the temperature during heating and cooling operations.
Many prior art thermostats have had various methods for accomplishing a limiting action, such as the limiting action shown in the Donald P. Kolbow U.S. Pat. No. 4,078,601, issued Mar. 14, 1978, and the Richard E. Fitzgerald, et al, U.S. Pat. No. 4,249,155, issued Feb. 3, 1981. In each of these patents, the thermostats have a single control point adjustment means for selecting the temperature with a changeover switch button or lever for activating the limiting action for either heating or cooling.
In a time controlled thermostat of the type disclosed in the Carl G. Kronmiller U.S. Pat. No. 2,558,617, issued June 26, 1951, the normally controlled temperature is selected by a first lever and the setback temperature is selected by a second lever. If the thermostat is to be used for heating only, as disclosed in the Kronmiller patent, the first lever can be fixed with a screw to prevent the normal temperature from being selected above a certain value. Obviously, if a changeover switch is used to modify a time controlled thermostat having two separate levers for setting the normal and the setback temperature of the thermostat with a changeover switch to provide for the control of both heating and cooling apparatus, the lever used for the normal temperature control point selection does not remain the same. In the T8082A Fuel Saver Thermostat manufactured and sold by Honeywell Inc. and shown in its Brochure 60-2416-2 of September 1979 when used with a Q682A Switching Subbase for heating and cooling such is the case. Since the lever for selecting the normal temperature control for heating and cooling changes from one lever to the other, the conventional manner of limiting the position of the lever used to select the normal control temperature, such as a set screw, could not be used. The limiting action changes depending upon whether the thermostat is in the heating or cooling operation.
The present invention is concerned with a time controlled thermostat having a first and a second temperature control point selection levers and a changeover switch lever to change the connection of the thermostat between heating and cooling apparatus. Limits are provided for one of the other of the first and second levers which are made effective by the changeover switch lever so that in the heating operation the first lever is limited in its movement for temperature selection, and in the cooling operation the second lever is limited in its movement for temperature selection.